Tubular heat exchangers with coiled tubes in combination with tie rods bracing the tube bottoms have been developed according to DE 36,40,970 C2 for the operation of high pressurizations on the casing under extremely high thermal loads acting at the same time.
In this heat exchanger structure, two thin-walled tube bottoms are connected via tension rods, which rods are arranged on concentric graduated circles.
The radial distance of the graduated circles is selected such that sufficient room for the heat exchanger tubes remains on the intermediary ring areas. These heat exchanger tubes are coiled on the greatest section of their length over the longitudinal axis of the container.
Due to the necessary elasticity of the coil with at least one winding, the external row of tubes determines the cylindrical length of the coiled area of all rows of tubes. Since the exchange surfaces of all tubes and thus the extended tube lengths should be as equal as possible, the coiled tubing on the graduated circles towards the center of the tube bottom has a number of windings greater than 1 with constant angle of inclination. The ends of the tubes are not coiled and run parallel to the longitudinal axis of the heat exchanger. The direction of rotation of the coiling changes from graduated circle to graduated circle.
The tie rods, around which coolant flows, are acted upon with the same temperature as the casing and are thus also subjected to the same heat expansions.
As a result of the flexibility of the coil, the tubes acted upon with higher temperatures only release small forces, created as a result of the heat expansion, as a load on the tube bottoms. Thus, by means of the combination of the bracings tie rods with the coiled tubes, high pressures can be absorbed by the casing and the highest temperatures can be absorbed by the tubes without damage.
Due to the narrow tube separations, there is no possibility in the area of the coiling of connecting the bundles of tubes of the individual graduated circles to one another, in order to bring about a necessary support among them or on the cylinder wall of the heat exchanger.
However, in a horizontal installation of the heat exchanger, since the weight of the bundles of tubes must be diminished, and even in a vertical installation, supports of the tubes are necessary to avoid vibrations, the tie rods arranged on the adjacent graduated circles lying towards the outside should also be referred to as holding elements and even as supporting elements of a bundle of tubes.